Interestingly, the Twins Rule 5 pick, Terry Doyle, returned to his old team, has incredibly similar numbers to Scott Diamond at AAA. Diamond does have a better ERA (1.3 Difference) while Doyle has better K/9 (2.4 diff). For walks,they're both under 2/9.
My point here is that, had they felt Doyle was worth the pick I would have preferred they give him a longer look. He could have been kept in the pen for a bit and could have added some possible depth, even if he is the same pitcher as Diamond.